Abstract
A first-principles approach is used to systematically investigate the role of sp2 and sp3 hybridized bonds on the structural, mechanical, and electronic properties in a new BN phase (denoted Hex-(BN)12). Hex-(BN)12 has the same number of sp2 and sp3 hybridized atoms. The calculated cohesion energy, phonon frequencies, and elastic constants unambiguously confirm the structural stability of this compound. Due to the different types of hybridization and B–N covalent bonds with ionic characteristics, Hex-(BN)12 has unequal bond lengths and bond angles in these hybrid orbitals. These cause the relative energetic stability to be slightly lower than c-BN and w-BN. The hardness of Hex-(BN)12 is estimated to range from 33 to 40 GPa. The bond-breaking order under stress is sp3–sp3, sp2–sp3, and sp2–sp2. DFT calculations with the gradient approximation (GGA) and HSE06 functional indicate the electronic structure contains an indirect band gap at 3.21 and 4.42 eV, respectively. The electronic states in the region near the Fermi level primarily arise from the 2p orbitals in sp2-hybridized atoms. In general, sp3 bonded B and N atoms guarantee higher mechanical properties, and sp2 bonded atoms ensure ductility and even conductivity, although all changes vary with spatial structure. Hex-(BN)12 can be obtained from multilayer yne-BN, and BN nanosheets, nanotubes and nanoribbons under pressure.
Highlights
Boron nitride (BN) is a group III–V compound that can theoretically exhibit a variety of frameworks because B and N atoms can form chemical bonds by means of sp, sp[2], and sp[3] hybridizations or combinations
The mechanical properties of these reported BN phases are different. c-BN and w-BN are typical superhard materials; M-BN is hard, while h-BN formed from sp2-hybridized atoms is more ductile and is widely used as a lubricant
Dynamic, and mechanical stability was unambiguously con rmed from calculations of the cohesive energy, phonon spectrum, and elastic constants. It can be obtained from multilayer yne-BN, nanosheets, BN nanotubes (BNNTs), and BN nanoribbons (BNNRs) under pressure
Summary
Boron nitride (BN) is a group III–V compound that can theoretically exhibit a variety of frameworks because B and N atoms can form chemical bonds by means of sp, sp[2], and sp[3] hybridizations or combinations. Examples include sp and sp[2] graphyne-BN (yneBN) and graphdiyne-BN (diyne-BN);[1,2,3,4,5] sp2-hybridized nanocages,[6,7,8] nanotubes,[9,10,11,12] nanoribbons[13,14] and nanosheets;[15,16,17,18] sp and sp[3] porous BN networks,[19] M-BN,[20] HBNFs,[21] and 3D BN allotropes from compressed single-walled BN nanotubes (BNNTs);[22] sp3-hybridized c-BN, bct-BN, Z-BN,[23] and O-BN.[24] They usually have high thermal conductivity, chemical stability, excellent mechanical properties, and unique electronic and optical properties, facilitating practical applications in the many elds related to hydrogen energy,[19,25,26] advanced It is worth noting these BN phases exhibit unique physical and chemical properties. The in uence of sp[2] and sp[3] hybridization on stability, hardness, and electronic properties is an interesting issue that is worth studying
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